Slipcasting with Paper Clay

[Ryan M Miller]

I am interested in building a plaster mold for an earthenware slipcast pot intended for cooking so I would like to know what temper materials would be suitable for a slip that won't settle to the bottom of a casting during the formation of the skin. Obviously, sand and grog don't qualify since they would settle in less than five minutes, but I am curious about the possibility of using paper pulp, dung, or other plant fibers as the temper material for the slip since organic fibers tend to suspend in water more readily than sand or grog. If any more experienced potters have successfully slipcasted with either stoneware or earthenware paper clay, please let me know. If paper clay is a viable option for slipcasting, then it means that I can make a stackable set of matching cooking pots more easily and faster than if I were to hand-build the pots or throw them on a wheel.

[Min]

By cooking pots do you mean pots for the oven or a gas stovetop?

[Kelly in AK]

Very much looking forward to hearing from the paper/organic clay slip casters.  Have you considered jiggering them? It doesn’t seem an any more more complicated path to reach nesting bowls with such particular clay body requirements. You’re already planning to make a mold. Sounds like you want production speed. Seriously though, what do you mean by “pot intended for cooking?”

[Ryan M Miller]

By pot intended for cooking, I mean one that will be used primarily on either a gas burner or bed of coals. It should function something like a Dutch oven if it were made of earthenware clay instead of cast iron. The pot must be able to withstand the thermal shock of heating and cooling during cooking so that it doesn't shatter easily even when heated slowly.

[Min]

I would suggest contacting New Mexico Clay and asking them about their micaceous clay, let them know you are looking into slip casting and if they have any info or experience with this as not all clays cast well. If they don't know I would ask if you could purchase some of their dry lowfire mica clay and start testing it. Can't speak to the paperclay addition as I haven't cast with it but I have read articles of people using fibres in the slip, my hunch is you wouldn't need it.

Sumi Von Dassow's book "The Potters Kitchen" would be a good resource for shapes, process etc.

19 hours ago, Ryan M Miller said:

it means that I can make a stackable set of matching cooking pots more easily and faster than if I were to hand-build the pots or throw them on a wheel.

How many pots are you talking about here, selling them commercially or just enough for your own use?

I'ld also make sure you have a really good insurance policy if these will be sold.

[PeterH]

You may find the results of a search for flameware in the Clay and Glaze Chemistry forum of interest.

[neilestrick]

I don't think a typical paperclay has enough fiber in it to open up the body in a way that would affect how it the body handles thermal shock. It would take a lot more fiber than is usually used to increase building strength. Fibers are tiny but have a big effect on greenware strength. I also don't think that opening up the body is the best way to go about it. You'd be better off using a body that can handle the thermal shock from a formula standpoint, as Peter and Min have indicated.

[Bill Kielb]

9 hours ago, Ryan M Miller said:

, I mean one that will be used primarily on either a gas burner or bed of coals

As others have said, paper clay is not necessarily shock resistant, and can be less dense in the end. I have made micaceous products and they are relatively porous and mostly coil and scrape and lots and lots of burnishing. Not really flame ware. I also experimented with flame ware and low expansion clays and compatible glazes just for the use.
My take, the flame ware works and most items were made relatively thick to be durable especially for direct contact. None of that rings of slip casting to me though. My suggestion is try some flame ware to see if it even fits your envisioned process and produces a durable end product to your satisfaction.

Edited October 24, 2022 by Bill Kielb

[Ryan M Miller]

It sounds like I'll definitely have to do a test fire first. I am aware of prehistoric potsherds that show plant fiber was used as a temper material in the piedmont of the United states. These pots were often fired in a pit fire so they would be subject to thermal shock at least during the initial firing. At least some of these potsherds are identified as belonging to cooking vessels Here is a link to a relevant journal article.

Unfortunately, these prehistoric pots would only have been hand built either with the coil and scrape method or the paddle and anvil method so the example pot sherds do not answer whether or not a fiber based temper will remain suspended in a slip during a slip cast or if the temper material will settle too fast.

 

[Bill Kielb]

38 minutes ago, Ryan M Miller said:

These pots were often fired in a pit fire so they would be subject to thermal shock at least during the initial firing. At least some of these potsherds are identified as belonging to cooking vessels Here is a link to a relevant journal article.

Seems like a nice bit of research to be had. Share your tests here if possible, it looks interesting.

[Kelly in AK]

Many areas of ceramics hold my interest personally, but not at all commercially. One of those is earthenware cooking pots. Not flameware as potters define it, but cookware as is used throughout the world, over an open flame. The United States doesn’t have (or has outgrown?) the culture necessary to understand their use. There are very few domestically who produce these for sale, coupled with significant marketing and education.  On the other hand, this kind of pottery is readily available as an import. “Chamba Ware” is available through Walmart.

I played around enough with it to make my own pots that work on the stove and understand that they’re unlike the pots I sell and unlike the pans I use regularly. Special maintenance required. Special cooking technique. Slow. Clean well with baking soda. No soap, ever.

All that said, the clay body came up with I still can’t say would slip cast, but felt it’s worth sharing. It has 40% non plastic ingredients that are relatively fine grained. It might work. 

I’ve cooked beans in this pot at least 30 times over the last six years. Broke the handle off the lid when I dropped it in the sink. It finally got a crack last year, not on the stove, but in the microwave. First world problems. Still using it. 

Redart clay- 40%

Kyanite 100 mesh- 30%

OM4 ball clay- 10%

Lincoln 60- 10%

Talc- 10%

Fired to Cone 06. 

[Jeff Longtin]

Years ago I worked with a potter who was using Domestic porcelain with nylon fiber. Thinking it would solve my warpage problem I decided to add nylon fiber to my cone 6 porcelain casting body. Other than making the slip thicker it really didn't affect usability all that much. (It also didn't improve warpage, on my larger flat forms, so I abandoned the practice.)

An alternative for you might be using hemp fiber. 

I am in agreement with others, however, and think you might have better luck developing a flameware body, and adjusting it into a casting body, rather than thinking about fiber alone.

[Ryan M Miller]

I have been reading more on slipcasting and it looks like I forgot to factor into account what material will be used as a deflocculant. I was unaware of the importance of adding sodium silicate, Darvan®, or washing soda to the slip. Now I'm wondering how these deflocculants could chemically react with organic temper materials, especially since wasing soda looks like the most readily available defloculant for me.

[Callie Beller Diesel]

I’m a lot less good with slipcasting, but I did use to do a LOT of work with paper clay. I think it would be possible to use a fine enough paper fibre in a casting slip. BUT.

Consideration number one: paper or plant fibre rots quickly if it remains wet, and it stinks like something truly unholy. This happens within a week, unless you add some kind of mould inhibitor. Even then, you’re only staving off the inevitable. If you choose to use paper in a casting slip, I recommend using it within a few days of mixing it.  Edited to add: I don’t know how the rotted fibre would affect how the slip deflocculates. You’ll have to keep an eye on that.

Consideration 2: Paper or plant fibres temper or open a clay body differently than the way sand or grog will. In societies where plant fibres were added to temper clay being fired in pits, the burn isn’t hot or clean enough to get rid of all of the material. If you’re firing pots in even a bisque level firing in a more contemporary kiln, the paper fibres burn out, leaving behind voids. This will leave your end piece more friable than it would be without the paper fibre. When you temper with sand or grog, it remains in the clay and acts like aggregate in cement to improve strength. 

In terms of deflocculants, you should be able to get pure soda ash, sodium silicate and darvan wherever you’re buying clay. Washing soda from the grocery store usually has other things in it that aren’t casting slip friendly. 

[Ryan M Miller]

I have asked a few other potters about alternative deflocculant materials. I will begin a new thread here shortly. Any admins may close the thread if they think it's necessary.

Edited November 12, 2022 by Ryan M Miller